Light modulating mirror devices have been developed in which a mirror or reflector is can be positioned at various locations to either direct the impinging light to one location or to direct the impinging light to another location.
When a voltage is applied to one region housing the mirror, the mirror is moved so that the impinging light is directed to a first location. When the voltage is removed or applied to another region housing the mirror, the mirror is moved so that the impinging light is directed to a second location.
Such a device can be implemented in a variety of optical applications. For example, U.S. Pat. No. 5,061,049, issued on Oct. 29, 1991, entitled “Spatial Light Modulator and Method,” describes an spatial light modulator with a movable mirror.
Spatial light modulators are transducers that modulate incident light in a spatial pattern corresponding to an electrical or optical input. The incident light may be modulated in its phase, intensity, polarization, or direction, and the light modulation may achieved by a variety of materials exhibiting various electrooptic or magnetoopotic effects and by materials that modulate light by surface deformation.
An example of a prior art single pixel of an electrostatic (rigid) movable mirror device is illustrated by FIG. 1. The pixel, generally denoted 20, is basically a plate (flap) covering a shallow well and includes silicon substrate 22, insulating spacer 24, metal hinge layer 26, metal plate layer 28, plate 30 formed in layers 26-28, and plasma etch access holes 32 in plate 30. The portions 34 & 36 of hinge layer 26 that are not covered by plate layer 28 form torsion hinges (torsion rods) attaching beam 30 to the portion of layers 26-28 supported by spacer 24. Electrodes 40, 42, 46, and 41 run between spacer 24 and substrate 22 and are isolated from substrate 22 by silicon dioxide layer 44.
The design of FIG. 1 allows that the plate metal be as thick as desired and the hinge metal be as thin as desired without the problems of step coverage of the hinge metal over the plate metal and that the spacer surface under the beam metal is not exposed to processing side effects which would arise if the hinge were formed as a rectangular piece on the spacer prior to deposition of the plate metal.
Pixel 20 is operated by applying a voltage between metal layers 26-28 and electrodes 42 or 46 on substrate 22: beam 30 and the electrodes form the two plates of an air gap capacitor and the opposite charges induced on the two plates by the applied voltage exert electrostatic force attracting beam 30 to substrate 22, whereas electrodes 40 and 41 are held at the same voltage as beam 30. This attractive force causes beam 30 to twist at hinges 34 and 36 and be deflected towards substrate 22.
FIG. 1 also indicates the reflection of light from deflected beam 30 as may occur during operation of a deformable mirror device. The deflection of beam 30 can be a highly non-linear function of the applied voltage because the restoring force generated by the twisting of hinge 34 is approximately a linear function of the deflection but the electrostatic force of attraction increases as a function of the reciprocal of the distance between the closest comer of beam 30 and substrate 22.
Although electrostatic movable mirror devices have been used, the conventional electrostatic movable mirror devices fail to realize many desired characteristics. For example, the conventional electrostatic movable mirror devices have a relatively slow speed of actuation and use a relatively large amount of energy for actuation. Moreover, the conventional electrostatic movable mirror devices have a relatively high voltage of actuation, are complicated to build, and are not necessarily scalable to very small sizes. Lastly, the conventional electrostatic movable mirror devices have a relatively small extinction ratio.
Therefore, it is desirable to provide a mirror device that has a relatively higher speed of actuation, lower energy of actuation, lower voltage of actuation, simpler to build, easier to scale to very small sizes, and/or larger extinction ratio. Moreover, it is desirable to provide a deformable mirror device that has a relatively higher speed of actuation, lower energy of actuation, lower voltage of actuation, simpler to build, easier to scale to very small sizes, and/or larger extinction ratio.